The Immigration Department maintains a Tasmanian detention centre remains temporary, despite a local mayor saying it will remain open.

Brighton Mayor Tony Foster says he has been told by high-level officials that the centre north of Hobart will remain open indefinitely.

Pontville was temporarily re-opened last month to house single men mainly from Afghanistan., but for the first time is now holding children.

A spokesman for the Immigration Minister, Chris Bowen, says about 85 unaccompanied minors aged between 15 and 18 arrived yesterday.

It is understood they have come from the Leonora detention centre in Western Australia.

Councillor Foster says he was told of the decision to stay open at a recent meeting with Immigration Department deputy secretary John Moorhouse.

"The information that's been provided to me is that Pontville will remain open for the long term now which I think Tasmanians generally support," he said.

"He informed me that Pontville had been re-designated to an "A-pod" which is an alternative place of detention rather than an immigration detention centre and the good news was that we would be for the longer term."

"It now seems that Mayor Foster has more detail than even the minister and the head of the department," he said.

The Tasmanian Premier, Lara Giddings, believes the Federal Government can see the benefits in keeping it open.

"I suspect that we will see the Pontville detention centre open for some time now," she said.

"The Australian government see this centre as being a lot more humane than some of the centres that have been established in the past which have been out in the back of nowhere, in the heat of the Australian desert."

The former army barracks can accommodate up to 400 people, including 260 children.

The arrival of unaccompanied children has upset a support group.

The Tasmanian Asylum Seeker Support Group's Emily Conlon is against the move.

"Young children are much more vulnerable as far as their mental health needs go," she said.

"We don't like to see any children in detention including unaccompanied minors.

"Australia is signatory to a number of conventions on rights of the child which prohibit arbitrary detention so this is very concerning news."

Councillor Foster says he also does not like to see children in mandatory detention but he does not expect the children to be at Pontville for long.

"It's not something we like to see, unaccompanied minors behind barriers, but nonetheless they're only likely to be here for about two months at a time and moved on."

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